I need some help with simpleFoam. Here is my problem... I am simulating airflow through the following structure.

The boundary conditions include zero pressure at the outlet (largest cylinder) and the eight inlets are prescribed a constant pressure of 13 pa. The problem converges with out a problem.

I have another mesh which consists of only three cylinders (subset of the above problem) as shown below.

Once again the outlet (largest cylinder) is maintained at zero and the two inlets are prescribed a pressure of 6 pa (this was the average pressure at the the same locations obtained from the first simulation). The problem does not converge. The solver setting remain the same as the first simulation.

Thanks for the suggestion. The mesh did produce good results for a simple positive pressure simulation (i.e, positive pressure at the inlet and 0 pressures at the outlets). It looks like it might be a problem with the boundary type that I am specifying in /0/p and /0/U file for the following steadystate case. What boundary conditions needs to be specified for the following case?

I am not sure about this. However, when I run my simulations I always prescribe a pressure on the outlet, a velocity on the inlet and have velocity on outet as zerogradient and pressure at inlet as zeroGradient.

Looking at your problem, I could suggest that you set either the inlet or outlet velocity at fixedValue and leave the other one as zeroGradient, but that's just me using my hunch.

Senthil: that is a possibility (84 is pretty high). Try increasing the nNonOrthogonalCorrectors value in you system/fvSolution dictionary. Or even better, try to make the mesh more orthogonal.

hi louis
what do you mean "try to make the mesh more orthogonal" ?
how should we make the mesh more orthogonal, if we use SnappHexMesh for doing th mesh, we should increase the "maxNonOrtho 45;" e.g to 65 or else?